WO2016097768A1

WO2016097768A1 - Electrochemical test device

Info

Publication number: WO2016097768A1
Application number: PCT/GB2015/054092
Authority: WO
Inventors: James Moffat; Damian Baskeyfield; Marco Cardosi; Christopher Leach
Original assignee: Inside Biometrics Limited
Priority date: 2014-12-19
Filing date: 2015-12-18
Publication date: 2016-06-23
Also published as: EP3234568A1

Abstract

An electrochemical test device for determining a concentration of an analyte in a fluid sample, the electrochemical test device comprising: a support layer; a conductor layer above the support layer, the conductor layer comprising a set of electrodes; a spacer layer above the conductor layer, the spacer layer defining a sample introduction channel for introducing the fluid sample to the set of electrodes; and a cover above the spacer layer for covering the top of the sample introduction channel; wherein the electrochemical test device comprises an air passageway for venting air from the sample introduction channel, and wherein the air passageway is formed below the spacer layer.

Description

Electrochemical Test Device

Technical Field

The present invention relates to electrochemical test devices such as test strips for determining the concentration of an analyte in a fluid sample. The present invention also relates to a method of manufacturing an electrochemical test device.

Background

In the field of diagnostic devices as used in the medical device industry, especially those used for analysing blood or other bodily fluid samples, it is often required for users to monitor biometrics such as the levels of certain chemicals, substances, or analytes present for example in their bloodstream. For instance diabetics in particular must regularly monitor the concentrations of glucose in their blood in order to determine if they are in need of insulin or sugar. In order to respond effectively to an individual's need to monitor blood sugar levels, diagnostic devices and kits have been developed over the years to allow an individual to autonomously determine the concentration of glucose in their bloodstream, in order to better anticipate the onset of hyperglycaemia or hypoglycaemia and take preventative action as necessary. Typically the patient will, using a lancing device, perform a finger stick to extract a small drop of blood from a finger or alternative site. An electrochemical test device, which is often a test strip, is then inserted into a diagnostic meter, and the sample is applied to the test strip. Through capillary action, the sample flows through a capillary channel across a measurement chamber of the device and into contact with one or more electrodes or similar conductive elements coated with sensing chemistry for interacting with a particular analyte or other specific chemical (for example glucose) in the blood sample. The magnitude of the reaction is dependent on the concentration of the analyte in the blood sample. The diagnostic meter may detect the current generated by the reaction of the reagent with the analyte, and the result can be displayed to the user.

Typically, such electrochemical test devices have a set of electrodes such as a counter/reference electrode and one or more working electrodes. Sensing chemistry is used which is typically tailored to the particular analyte of interest. For example, when measuring the concentration of glucose in a sample, a glucose oxidase or a glucose dehydrogenase enzyme can be used in conjunction with a mediator such as potassium ferricyanide. The skilled person will understand that different electrochemical test devices, electrode arrangements and sensing chemistry may be used.

The present invention seeks to provide an improved electrochemical test device.

Summary

In order for a sample to flow across a measurement chamber of an electrochemical test device through capillary action, an opening is typically required to allow the air inside the capillary channel to escape in order for the fluid to flow and fill the channel. The current accepted method of venting a capillary channel in a test strip is to manufacture an assembly of punched and cut tape layers of various geometries to provide slots, holes and passages connected to the capillary channel to allow the air to vent. The inventors have recognised that this approach requires complex cutting, lamination and registration steps each with its own set of tolerances and limitations. Furthermore, such complex cutting techniques may weaken the overall structure of some material layers, such as cut tape layers, within the electrochemical test device, leading to potential variation and defects in the electrochemical test device assembly and potential leakage of the sample from the device. Additionally, the location of such holes and passages in the device sometimes lead to confusion amongst users, who may attempt to provide a fluid sample to an air passageway as opposed to the capillary channel. In accordance with an aspect of the invention there is provided an electrochemical test device for determining a concentration of an analyte in a fluid sample. The electrochemical test device comprises a support layer. The electrochemical test device further comprises a conductor layer above the support layer, the conductor layer comprising a set of electrodes. The electrochemical test device further comprises a spacer layer above the conductor layer. The spacer layer defines a sample introduction channel for introducing the fluid sample to the set of electrodes. The electrochemical test device further comprises a cover above the spacer layer for covering the top of the sample introduction channel. The electrochemical test device also comprises an air passageway for venting air from the sample introduction channel. The air passageway is formed below the spacer layer. By providing an air passageway below the spacer layer, there is no need for a venting system in either the spacer layer itself or in a layer above the spacer layer. Accordingly, the disclosed electrochemical test device abolishes the need for complex cutting techniques used in the prior art for forming air vents. Instead, the air passageways may be formed in the lower layers of the electrochemical test device. That is, the lower layers, such as the conductor layer, may have a dual purpose. Firstly the conductor layer may provide the means for measuring the concentration of an analyte in a fluid sample by providing a set of electrodes for applying a potential difference across the fluid sample. Secondly, the conductor layer may be patterned so as to form channels, grooves and ducts for venting air from the electrochemical test device.

The electrochemical test device may be a biosensor. The electrochemical test device may have a longitudinal axis, and the air

passageway may be arranged for venting air primarily in the direction of the longitudinal axis. Accordingly, air may be vented away from the sample introduction channel of the device towards an opposite end of the device. In this way, an outlet for the air passageway may be provided at a distal end of the electrochemical test device from the sample collection end, thereby reducing user confusion as to which aperture a fluid sample should be supplied.

The sample introduction channel may be arranged to run primarily in the direction of the longitudinal axis.

The support layer may be a substrate.

The conductor layer of the electrochemical test device may further comprise a set of conductive tracks, each conductive track of the set of conductive tracks being electrically coupled to a corresponding electrode of the set of electrodes. The conductive tracks may extend from the set of electrodes, along the longitudinal axis of the electrochemical test device. The conductive tracks may be connected to an electronic device, such as a meter, for determining a concentration of an analyte in a fluid sample. The conductive tracks may be used to provide a potential difference between electrodes of the set of electrodes and may thereby be used to provide a potential difference across a fluid sample for generating an output signal from the fluid sample. The air passageway may be disposed between conductive tracks of the set of conductive tracks. Accordingly, the air passageway may vent air between the conductive tracks of the set of conductive tracks.

The width of the air passageway may be narrower than a width of the sample introduction channel. The height of the air passageway may be smaller than a height of the sample introduction channel.

The air passageway may be provided with a plurality of upstands. The plurality of upstands may be suitable for providing a plurality of venting routes within the air passageway. The venting routes allow for air to vent from the electrochemical test device along multiple paths. Accordingly, even in the event of a closure or blockage of one path, the air can escape from the sample introduction chamber along other paths. For this reason, even in the event of a manufacturing fault or heavy handling of the electrochemical test strip by, for example, a user, the venting action of the electrochemical test strip can still function, thereby assisting in the capillary action relied upon for drawing fluid into the sample introduction channel. The upstands may provide structural support between layers of the device.

The lower surface of the cover may have hydrophilic properties. That is, the surface of the cover which is exposed to a fluid sample inside the sample introduction chamber may have hydrophilic properties. The hydrophilic properties of the lower surface of the cover can assist in drawing fluid into the sample introduction channel.

The layers may be formed by any suitable manufacturing technique.

The spacer layer may comprise an adhesive having hydrophobic properties. For example, the spacer layer may comprise double sided adhesive tape. The

hydrophobic properties of the adhesive may assist in hindering the flow of the fluid into the air passageway from the sample introduction chamber. The tape may comprise polymer layers. The tape may comprise a laminated assembly construct. The tape may be made of any suitable material.

The conductor layer may be a printed layer. The thickness of the conductor layer may define, at least in part, a height of the air passageway. In this way, the conductor layer performs the dual role described above. The electrochemical test device may further comprise an insulator layer above the conductor layer and below the spacer layer. The insulator layer may define an area in which at least a part of the set of electrodes is exposed to the sample introduction channel. The thickness of the insulator layer may define, at least in part, a height of the air passageway. Additionally or alternatively, an air passageway may be provided by an air passage layer above the insulator layer and below the spacer layer. The air passageway may comprise a plurality of upstands for providing a plurality of venting routes within the air passageway. In this way, an insulator layer may, in conjunction with the conductor layer, assist to guide air out of the sample introduction channel.

The insulator layer may be a printed layer.

The air passageway may be configured for venting air from the sample introduction channel into a sealed chamber within the electrochemical test device. By providing a sealed chamber into which the air may flow, the requirement of an external outlet for the air is no longer required. Accordingly, there is reduced confusion in users of the device, who cannot, for example, accidentally supply a fluid sample to the outlet of an air passageway. The electrochemical test device may comprise a substrate. The conductor layer may be provided above the substrate.

According to an aspect of the present disclosure, a method is provided for manufacturing an electrochemical test device. The method comprises providing a support layer. The method further comprises providing a conductor layer above the support layer, the conductor layer comprising a set of electrodes. The method further comprises providing a spacer layer above the conductor layer. The spacer layer defines a sample introduction channel for introducing the fluid sample to the set of electrodes. The method further comprises providing a cover above the spacer layer for covering the top of the sample introduction channel. The electrochemical test device comprises an air passageway for venting air from the sample introduction channel. The air passageway is formed below the spacer layer.

Sensing chemistry is typically provided on one or more of the electrodes of the electrochemical test device. The conductor layer of the electrochemical test device may further comprise a set of conductive tracks, each conductive track of the set of conductive tracks being electrically coupled to a corresponding electrode of the set of electrodes. The layers may be provided using any suitable manufacturing technique.

Providing a conductor layer may comprise printing the conductor layer. Providing a spacer layer may comprise applying tape. Providing a cover may comprise applying tape. The tape may comprise polymer layers. The tape may comprise a laminated assembly construct. The tape may be made of any suitable material.

The method may further comprise providing an insulator layer above the conductor layer and below the spacer layer. Providing an insulator layer may comprise printing the insulator layer.

The air passageway below the spacer layer may comprise an air passageway layer above the insulator layer and below the spacer layer. The air passageway may comprise a plurality of upstands. The upstands provide a plurality of venting routes within the air passageway. The upstands may also provide structured support to the device.

Throughout this specification, reference is made to directional terms such as "above" and "below", or "upper" and "lower". References made to such terms are purely indicative of relative positions of the features of embodiments disclosed herein. For example, wherever there is mention of a cover above a spacer layer and an air passageway below the spacer layer, the skilled person would understand that the cover and the air passageway are formed on opposite sides of the spacer layer. That is, directional terms such as those described herein do not refer to a direction relative to a viewpoint of an observer, but instead should be considered in all aspects as relative terms.

Other aspects and features of the present invention will be appreciated from the following description and the accompanying claims. Brief Description of the Drawings

Embodiments of the invention shall now be described, by way of example only, with reference to the drawings in which: Figure 1 shows a strip-meter system;

Figure 2 shows an exploded view of an electrochemical test device;

Figure 3 shows a perspective view of some of the layers of the

electrochemical test device shown in Figure 2;

Figure 4 shows a cutaway perspective view of some of the layers of the electrochemical test device shown in Figure 2;

Figure 5 shows an exploded view of an electrochemical test device;

Figure 6 shows a perspective view of some of the layers of the

electrochemical test device shown in Figure 5;

Figure 7 shows a perspective view of some of the layers of the

electrochemical test device shown in Figure 5;

Figure 8 shows a perspective view of some of the layers of the

electrochemical test device shown in Figure 5;

Figure 9 shows a perspective view of some of the layers of the

electrochemical test device shown in Figure 5;

Figure 10 shows a perspective view of the electrochemical test device shown in Figure 5;

Figure 1 1 shows a cutaway side view of the electrochemical test device shown in Figure 10;

Figure 12 shows an exploded view of an electrochemical test device;

Figure 13 shows a perspective view of some of the layers of the

electrochemical test device shown in Figure 12; and

Figure 14 shows a perspective view of some of the layers of the

electrochemical test device shown in Figure 12;

Figure 15 shows a cutaway side view of some of the layers of the electrochemical device shown in Figure 14;

Figure 16 shows an exploded view of an electrochemical test device; and Figure 17 shows a perspective view of some of the layers of the

electrochemical test device shown in Figure 16.

Throughout the description and the drawings, like reference numerals refer to like parts.

Detailed Description

The present invention seeks to provide an improved electrochemical test device for determining a concentration of an analyte in a fluid sample. Whilst various embodiments of the invention are described below, the invention is not limited to these embodiments, and variations of these embodiments may be made without departing from the scope of the invention. Figure 1 shows a strip-meter system 10. System 10 comprises a meter 12 for receiving an output signal from an electrochemical test device such as

electrochemical test strip 14. Electrochemical test strip 14 comprises a set of electrodes which typically comprises one or more working electrodes (not shown) and a counter/reference electrode, each of the working electrodes provided with sensing chemistry for reacting with at least one analyte of a fluid sample to be applied to electrochemical test strip 14. In this example, each of the one or more working electrodes has a reagent coated thereon. The counter/reference electrode may also have a reagent coated thereon. Meter 12 comprises receiving means 13 for receiving electrochemical test strip 14 and applying a potential difference to the working electrode(s) and the counter/reference electrode.

Meter 12 further comprises processing circuitry 15 for carrying various functions relating to the operation of meter 12. For example, processing circuitry 15: controls operation of receiving means 13 so as to control application of a potential difference between the working electrodes and the counter/reference electrode; processes one or more output signals generated at test strip 14; controls the display of messages on display 18; etc. Meter 12 further comprises first and second memory storages 16a and 16b. Although two memory storages are shown, in other embodiments the memory storages may be combined to form a single memory storage, or meter 12 may comprise more than two memory storages. Meter 12 also comprises a display 18 for displaying readouts of measurements taken by meter 12.

When manufacturing an electrochemical test device such as electrochemical test strip 14 a multitude of layers may be overlapped to provide various functions such as conductive tracks, electrode area definition and positioning of chemistry. These layers not only have a length and width dimension but also a thickness. The inventors have recognised that it is possible to take advantage of this thickness dimension to pattern the layers in order to provide a series of passageways/channels and upstands.

Figure 2 shows an exploded view of an electrochemical test device according to a first example. This example will be described in relation to a received blood sample, although the skilled person would appreciate that the electrochemical test device could be used with any suitable fluid sample.

The electrochemical test device comprises a support layer 210. In this example the support layer is referred to as substrate 210. Substrate 210 has a thickness of around 0.35mm. The substrate, in this example, is made from a polyester, although the skilled person would understand that any suitable substrate may be used. The substrate is thermally/dimensionally stable, with consistent properties such as thickness, surface roughness and surface energy.

Above the substrate 210 is the conductor layer 212. In this example, the conductor layer 212 is directly disposed upon the substrate 210 using carbon based ink. In this example, the conductor layer 212 is printed directly onto the upper surface of the substrate 210. The conductor layer may be printed onto the substrate 210 using screen printing, lithographic printing, tomographic printing, or any other suitable method of printing. The conductor layer comprises a set of electrodes including working electrode 214 and reference electrode 216. The conductor layer further comprises a set of conductive tracks 217. In this example, the conductive tracks extend along the longitudinal axis of the electrochemical test device.

Sensing chemistry for interacting with a particular analyte is provided on each electrode of the set of electrodes. In this example, the working electrode 214 and the reference electrode 216 are coated in a reagent for interaction with an analyte to be measured. As an example, for measuring the concentration of glucose in a blood sample, a glucose oxidase or a glucose dehydrogenase enzyme can be used in conjunction with a mediator such as potassium ferricyanide.

Above the conductor layer 212 is an insulator layer 218. The insulator layer 218 is made of an electrically insulating material, and is directly disposed upon the upper surface of the conductor layer 212. The insulator layer 218 is, in this example, made of a dielectric material and defines an interaction area. That is, the insulator layer 218 electrically insulates some portions of the conductor layer 212 from the layers situated above in the electrochemical test device. Specially designed gaps in the insulator layer 218 expose some portions of the conductor layer 212 to the layers situated above in the electrochemical test device. Reagent layers coat exposed electrode interaction areas which are not shown in Figure 2 for sake of clarity. In this way, the insulator layer 218 defines which part or parts of the electrodes of the conductor layer are able to come into contact with an applied blood sample for the measurement of the analyte (e.g. glucose).

Above the insulator layer 218 is a spacer layer 220 formed of a polyester core. The spacer layer 220 defines a sample introduction channel 222, or measurement chamber, for introducing a blood sample to the conductor layer 212. The height of the sample introduction channel 222 is defined by the thickness of the spacer layer 220. The spacer layer 220 is formed of double sided adhesive tape which, in this example, is applied directly to the upper surface of the insulator layer 218. The sample introduction channel 222 is formed by providing a gap into the double sided adhesive tape of the spacer layer. The thickness of the spacer layer is approximately 0.1 mm, which provides a good balance between the volume of the sample introduction channel and the performance of the electrochemical test device. Above the spacer layer 220 is a cover layer 224. The cover layer 224 acts as a ceiling to the sample introduction channel 222, thereby closing the sample

introduction channel 222 from above. The cover layer 224 is formed of single sided tape and, in this example, is adhered directly to the upper surface of the spacer layer 220. The lower surface of the cover layer 224 had hydrophilic properties, which assist in drawing a blood sample into the sample introduction channel 222.

In use, a blood sample is applied to the sample introduction chamber 222 of the electrochemical test device. Through capillary action, the blood is drawn into the sample introduction channel 222 to the electrodes 214 and 216 of the conductor layer 212. That is, the sample introduction channel acts as a capillary channel. A potential difference is applied across the electrodes 214 and 216 and the blood sample, and an output signal such as a transient current is generated from the blood sample. The characteristics of the output signal can be used to determine the concentration of an analyte, such as glucose, in the blood sample.

Figure 3 shows a perspective view of some of the layers shown in the example of Figure 2. In particular, the substrate 210, the conductor layer 212 and the insulator layer 218 are depicted. As can be seen in Figure 3, the insulator layer 218 covers only a part of the conductor layer 212, leaving a part of the conductor layer 212 exposed to the spacer layer 220 situated above (not shown in Figure 3). Accordingly, the insulator layer 218 defines an interaction area 312 in which the set of electrodes 214 and 216 of the conductor layer 212 are exposed to the above layers e.g. sensing chemistry / reagent layers (not shown) and, in particular, to any blood entering the sample introduction channel 222, able to interact with the sensing chemistry / reagent layers and exposed electrode areas directly.

In this example, an air passageway 310 is formed in part by the conductor layer 212. The air passageway 310 is suitable for venting air out of the sample introduction channel 222 to allow a blood sample to enter the sample introduction channel 222 via capillary action. Accordingly, the air passageway 310 is smaller than the sample introduction channel 222. In particular, the air passageway is narrower than the sample introduction channel 222 and has a smaller height than the sample introduction channel 222 so that air may easily travel along the air passageway 310 but blood or any other fluid will not easily be able to travel along the air passageway.

The air passageway 310 vents air along a longitudinal axis of the electrochemical test device, away from the inlet of the sample introduction channel. In this way, the air passageway outlet, from which air may escape from the electrochemical device, is not located near to the sample introduction inlet, to which a blood sample is provided. As a result, there is less user confusion as to where to apply a blood sample. In particular, the air passageway 310 vents air between the conductive tracks 217 of the conductor layer, towards an end of the electrochemical test device that may be coupled to a meter 12 in use. As can be seen in Figure 3, the air passageway 310 is formed by patterning the conductor layer 212. A thickness 314 of the conductor layer 212 defines, at least in part, a height of the air passageway 310. A thickness 316 of the insulator layer also contributes to the size of the air passageway 310. The air passageway 310 is sealed from above by the double sided adhesive tape of spacer layer 220. That is, the floor of the air passageway 310 is formed by the substrate 210, the walls of the air passageway is formed by the thickness 314 of the conductor layer 212 and the thickness 316 of the insulator layer 218, and the ceiling of the air passageway 310 is defined by the lower surface of the spacer layer 220.

Figure 4 shows some of the layers shown in Figure 2 cut away along a longitudinal axis of the electrochemical test device. In particular, Figure 4 shows the substrate 210, the conductor layer 220, the insulator layer 218 and the spacer layer 220. The top tape spacer 220 adheres to the dielectric print of the insulator layer 218, forming the sample introduction channel 222 which acts as a capillary channel. As can be seen in Figure 4, the air passageway 310 is covered over by the spacer layer 220. The restricted height of the conductor layer 212 and the hydrophobicity of the adhesive on the lower surface of the spacer layer form a fluid break which hinders the progress of fluid along the air passageway 310. Accordingly, in use, blood may enter the sample introduction channel 222 and proceed via capillary action to flow to the electrodes 214 and 216 of the conductor layer 212, but flow will be impeded at the air passageway 310.

Figure 5 shows an exploded view of an electrochemical test device according to a second example. In the second example, the electrochemical test device comprises a support layer 510. In this example, the support layer 510 is referred to as substrate 510. On top of the substrate 510 is printed a conductor layer 512 comprising a set of electrodes including working electrode 514 and a reference electrode 516 for applying a potential difference across a fluid sample. The working electrode 514 and the reference electrode 516 function in much the same way as the electrodes discussed above in relation to Figures 2-4. The conductor layer 512 further comprises a set of conductive tracks 517.

In this example, a series of upstands 518 are printed at the conductor layer 512. Although formed of the same conducting ink as the electrodes 514 and 516, the upstands 518 are not coupled to any electrical source and so do not conduct electricity within the electrochemical test device. The upstands are rectangular and arranged in a matrix, although, of course, they may be of any suitable shape and configuration. Any number of upstands may be provided and the matrix may be of any size. Accordingly, air may travel along multiple paths, which prevents the chance that a blockage or occlusion as a result of a manufacturing defect or aggressive handling will prevent sufficient venting of air from the electrochemical test device.

The upstands 518 define a primary air passageway 520 along the longitudinal axis of the electrochemical device. Additionally, the upstands 518 define a number of alternative venting routes 522, substantially perpendicular to the primary air passageway 520. In this example, the upstands are used to define a number of cross-connecting air passageways. Accordingly, in use, air travels along the primary air passageway 520 and the secondary air passageways (the venting routes 522) as the blood sample is introduced to the electrochemical test device. The upstands thereby provide a greater venting volume and so assist in allowing a faster filling of the sample introduction channel.

An insulator layer 524 is directly disposed upon the conductor layer 512. As in the example shown in Figures 2-4, the insulator layer 524 defines an interaction area in which the electrodes of the conductor layer 512 are exposed to the layers situated above. Additionally, a further series of upstands 526 are printed at the insulator layer 524. The upstands 526, in combination with the upstands 518 define the height of the primary and secondary air passageways. The upstands 526 are printed using the same dielectric material as the rest of the insulator layer 524. Directly above the insulator layer 524 is, in this example, the spacer layer 528, the spacer layer 528 having a sample introduction channel 530 or measurement chamber. As in the first example described above, the spacer layer 528 is formed of double sided adhesive tape. The combined upstands 518 and 526 further assist in preventing the tape layer 528 from collapsing and sealing the air passageway. The rigidity and thickness of the spacer tape can be optimised for supporting the spacer layer. For example, the more rigid or thick the spacer layer is, the further apart the upstands can be positioned increasing the venting volume and ability to configure and control the fill speed of the fluid sample when applied into the introduction channel 530 and across the sample chamber. Accordingly, the electrochemical test device is made more robust by the inclusion of the upstands.

Figure 6 shows a close-up perspective view of some of the layers of the example depicted in Figure 5. In particular, Figure 6 shows conductor layer 512 disposed directly upon the substrate 510. Insulator layer 524 is also shown.

Figure 7 shows a close up perspective view of some of the layers of the example depicted in Figure 5. In particular, Figure 7 shows the insulator layer 524 directly disposed upon the conductor layer 512. The upstands 526 of the dielectric layer 524 are printed directly upon the upstands 518 of the conductor layer 512. Accordingly, the height of the resultant air passage in the electrochemical test device is the height of the conductor layer upstands 518 plus the height of the insulator layer upstands 526. Figure 8 shows a perspective view of some of the layers of the example depicted in Figure 5. In particular, Figure 8 shows the spacer layer 528 directly disposed upon the insulator layer 524. The thickness of the spacer layer 528 and the thickness of the insulator layer 524 together define a height of the capillary channel/measurement chamber. The spacer layer 528 forms a ceiling to the air passage below, resting on the upstands 526 of the insulator layer 524. As with the first example, a hydrophobic adhesive is provide on the lower surface of the tape spacer layer 528. Figure 9 shows a perspective view of some of the layers of the electrochemical device depicted in Figure 5. The spacer layer 528 is shown in a transparent manner so as to provide a view of the layers beneath. The spacer layer 528 is affixed to the top of the insulator layer 524. A thickness of the spacer layer 528 defines a height of the sample introduction channel 530.

Figure 10 shows a perspective view of the assembled electrochemical test device according to the example shown in Figure 5. In Figure 10, the cover 532 is affixed to the top of the spacer layer. Figure 1 1 shows the example device of Figure 10 cut away along a longitudinal axis of the electrochemical test device.

Figure 12 shows an exploded view of an electrochemical test device according to a third example. In this example, a further air passage layer 1222 is included.

The electrochemical test device of the third example comprises a support layer 1210. In this example, the support layer is referred to as substrate 1210 and performs the same functions as those described earlier with reference to the first and second examples. Above the substrate 1210 is the conductor layer 1212 comprising a working electrode 1214 and a reference electrode 1216. The electrodes are provided with some sensing chemistry, such as a reagent, for interacting with an analyte. The conductor layer further comprises a set of conductive tracks 1217.

Above the conductor layer 1212 is the insulator layer 1218. As in the previously described examples, the insulator layer 1218 defines an interaction area 1220 for interactions between the electrodes of the conductor layer 1212 and a fluid sample applied to the electrochemical test device. In this example, the insulator layer 1218 covers the conductor layer everywhere except for at the rectangular slot 1220.

Above the insulator layer, an air passage layer 1222 is provided. The air passage layer 1222 comprises a series of rectangular upstands 1224 arranged in a matrix formation. The upstands 1224 of the air passage layer 1222 are deposited onto the upper surface of the insulator layer 1218 and may be formed of the same material as the insulator layer 1218 or formed of a different material. In this example, the upstands 1224 are deposited onto the upper surface of the insulator layer 1218 by printing.

As in the second example, the upstands 1224 define an air passageway having primary and secondary air passages. That is the air passageway provided by the air passage layer 1222 comprises a plurality of upstands 1224 which provide a plurality of venting routes within the air passageway.

By providing a separate venting layer 1222, the height of the air passageway is less restricted by manufacturing requirements, as the upstands 1224 can be printed to a desired thickness as required. Furthermore, the provision of a separate air passage layer 1222 allows air to travel along many paths in the electrochemical device. For example, the air is able to diffuse or vent through cross-connecting paths that extend laterally within the device. Accordingly, there is a reduced chance that a blockage or occlusion could prevent sufficient venting from the electrochemical test device.

Additionally, by providing a separate layer for the air passageway, the placement of the upstands 1224 is not restricted by the placement of, for example, electrodes in the conductor layer 1212.

Above the air passage layer 1222, a spacer layer 1226 formed of double sided adhesive tape is provided. The spacer layer 1226 has a sample introduction channel 1228 for introducing a blood sample to the conductor layer 1212. Additionally, spacer layer 1226 comprises a fold 1230 which allows the spacer layer 1226 to sit over the upstands of the air passage layer 1222. The sample introduction channel 1228 extends towards the entry of the air passageway as shown in the Figure so that air may vent from the sample introduction channel as the electrochemical test device receives a blood sample. Above the spacer layer 1226, a cover layer 1232 is provided. The cover layer 1232 provides a ceiling to the sample introduction channel 1228. The lower surface of the cover layer 1232 has hydrophilic properties, thereby assisting in the drawing of a fluid into the sample introduction channel 1228. The cover may comprise adhesive tape. As with the spacer layer 1226, the cover layer 1232 has a fold 1234 which allows the cover 1232 to follow the curves and contours of the spacer layer 1226 beneath.

Figure 13 shows a perspective view of some of the layers of the example depicted in Figure 12. In particular, Figure 13 shows the upstands 1224 of the air passage layer 1222 directly disposed upon the insulator layer 1218. The height of the upstands 1224 defines a height of the air passage formed by the air passage layer 1222.

Figure 14 shows a perspective view of some of the layers of the electrochemical test device according to the third example. In particular, in Figure 14 features of the substrate 1210, the conductor layer 1212, the dielectric layer 1218 and the spacer layer 1226 can be seen (cover layer 1232 not shown). The sample introduction channel 1228 of the spacer layer 1226 is shown to extend such that air may pass among the upstands 1224 of the air passage layer beneath. Accordingly, when a fluid enters the sample introduction channel 1228, air can vent from the sample introduction channel 1228 via the air passage layer 122. The fluid sample can then progress, via capillary action, to the exposed surfaces of the set of the electrodes of the conductor layer 1212.

Figure 15 shows the example device of Figure 14 cut away along a longitudinal axis of the electrochemical device.

Figure 16 shows an exploded view of an electrochemical test device according to a fourth example. This example is much like the example of Figures 2-4 except that, in this example, air is vented from the measurement chamber into a sealed chamber 1620.

The electrochemical test device of the fourth example comprises a support layer 1610. In this example, the support layer is referred to as substrate 1610 and performs the same functions as those described earlier with reference to the first, second and third examples. Above the substrate 1610 is the conductor layer 1612 comprising a working electrode 1614 and a reference electrode 1616. The conductor layer further comprises a set of conductive tracks 1617. Directly above the conductor layer 1612, in this example, is the insulator layer 1618. The insulator layer 1618 defines a sealed chamber 1620 into which air may be vented in use. Accordingly, in this example there is no vent access to the

atmosphere. As there is no separate external vent, user confusion concerning which aperture a fluid sample should be applied to is avoided.

A spacer layer 1622 is disposed upon the insulator layer 1620. The spacer layer 1622 defines a sample introduction channel 1624, into which a sample may be introduced for interaction with the electrodes of the conductor layer 1612. The sample introduction channel 1624 does not extend as far as the opening of the sealed chamber and, accordingly, air may enter the sealed chamber 1620 through the narrow neck of the insulator layer 1618 but a fluid is hindered from entering the chamber 1620. As with the above examples, in this example the spacer layer 1620 comprises double sided adhesive tape having a hydrophobic adhesive on the upper and lower surfaces. Accordingly, the adhesive further hinders the progress of a fluid into the sealed chamber.

The electrochemical test device is finished with a cover 1626, placed directly above the spacer layer 1622. The cover functions as a ceiling to the sample introduction passage. The lower side of the cover had hydrophilic properties, thereby assisting the drawing in of a fluid into the sample introduction channel 1624.

Figure 17 shows some of the layers of an electrochemical device according to a fourth example. In Figure 17, the substrate 1610, the conductor layer 1612 and the insulator layer 1618 can be seen. Not shown in Figure 17 are the spacer layer and the top cover layer. The spacer layer defining the sample introduction

channel/chamber and covering over the top of the sealed chamber in the insulator layer 1614.

The sealed chamber is large enough in volume that the pressure change brought about by the capillary forces pushing the air from sample introduction chamber (not shown in Figure 17) is a small enough percentage that it will not reduce or stop the sample introduction chamber from filling.

Variations of the described embodiments are envisaged, for example, the features of all the disclosed embodiments may be combined in any way. For example, an electrochemical test device may contain more layers than those disclosed in the preceding description. For example, an electrochemical test device may further comprise one or more bonding layers for bonding together one or more of the layers disclosed above. Additionally, some of the layers are not always necessary. For example, the insulator layer may be absent from the examples discussed above. The spacer layer may define the interaction area of the electrodes of the conductor layer beneath. The spacer layer may perform the dual role of receiving a fluid sample through a capillary channel and defining an interaction area for combining the fluid sample with the conductor layer. For example, the spacer layer can, with appropriate adhesive, define the active area/interaction area of the electrodes.

In the examples discussed above, a layer structure has been shown. The order in which each of the layers is formed may vary and any layer may, in some way, be configured so as to be in contact with any other layer.

The fluid sample may be a biological fluid. For example, the biological fluid may be blood, or may be interstitial fluid, or may be plasma. The analyte may be any analyte found in the fluid sample. For example, the analyte may be glucose, lactate, glycerol, cholesterol, or a ketone such as β-hydroxybutyrate.

The electrochemical test device may be any suitable electrochemical test device. The electrochemical test device may be a test strip. In some examples the

electrochemical test device may comprise a patch. Electrochemical test devices such as patches typically comprise a subcutaneous fluid extraction set and sensing chemistry for interaction with the analyte. The electrochemical test device may be a monitoring component which transmits an output signal to a separate device such as a meter, either wirelessly or through a wired connection. The electrochemical test device may comprise a continuous monitoring device or a semi-continuous monitoring device.

The electrochemical test device may be suitable for testing for multiple analytes. For example, the conductor layer may comprise a number of electrodes, each electrode featuring different sensing chemistry for detecting a different analyte. In particular, for each analyte there may be a dedicated electrode of the conductor layer coated in a particular reagent suitable for reacting with the analyte. In the examples provided above, the conductor layer and the insulator layer are printed layers. The conductor layer and the insulator layer may be supplied using any suitable manufacturing technique. These include forms of printing, for example, screen printing, lithographic printing or tomographic printing. The conductor layer and the insulator layer need not be provided in the same way. Other suitable

manufacturing techniques include etching, and/or sputtering, chemical vapour deposition or physical vapour deposition. A conductor layer may be formed of any suitable conductor. For example, the conductor layer may be formed from a carbon based paste, such as a carbon /graphite paste, including graphene. The conductor layer may be formed of one or more metal based paste such as a gold, platinum or silver paste. The conductor layer may be of any suitable thickness. For example, the conductor layer may have a thickness greater than or equal to 0.005mm and less than or equal to 0.030mm.

The insulator layer may be formed of any suitable insulating material. For example, dielectric/insulation inks may be polymer loaded inks that are thermoplastic, thermoset or UV cured and that, when dried or cured, form a contiguous non- conductive layer. Examples include, LOCTITE EDAG PF 021 E&C and DuPont 5018.

In the examples discussed above, a polyester substrate layer was featured. Suitable substrate materials include polyester, polyimide, polystyrene, PVC, polycarbonate, glass and ceramic. When other layers are to be printed onto the substrate layer, the substrate layer has to be suitably printable for the chosen inks. The substrate must also be non-conductive. Typical thicknesses of the substrate layer range from 0.1 mm to 0.5mm e.g. 0.35mm. Glass and ceramic can be thicker as these are easier to handle with increased thickness. Thinner polymer substrates may be more difficult for the end user to use. Thicker substrates may offer some handling benefits.

The spacer layer may be formed of any suitable material. For example, the spacer layer may be made from a polyester core with a thin layer of PSA (Pressure Sensitive Adhesive) on either side. These adhesives can be the same or different depending on which layer is to be adhered to which side of the spacer layer.

Although in the examples above the thickness of the spacer layer was 0.1 mm, the thickness may vary. A typical range for the spacer layer thickness is 0.005 - 0.030mm. Lower thicknesses may affect sensor performance and higher thicknesses would increase the volume of the sample introduction channel. Thicker spacer layers would be able to bridge over the gaps between upstands more rigidly, thereby reducing the chance of a closure of a venting route. A thickness of an adhesive on the spacer layer may contribute to the rigidity of the spacer layer.

Typically a spacer layer has a high volume resistivity. For example the volume resistivity may be greater than 1χ10⁹Ωαη. Other variations of the spacer layer are envisaged. For example, the spacer layer may not feature a substantially hydrophobic element. In some examples, the spacer layer is, at least in part, more hydrophobic than a layer directly above the spacer layer and a layer directly below the spacer layer. In some of the examples discussed above, a plurality of upstands is provided. The upstands may be of any suitable shape and configuration. For example, the upstands may be substantially rectangular (cuboidal) or may be circular (cylindrical). The upstands may not have a uniform shape, and may be of different shapes suitable for supporting a layer above and for providing venting routes. The upstands may be positioned in such a way as to form regular or irregular venting routes.

Any upstands provided in the conductor layer or the insulator layer may be formed as a separate step in manufacture. For example, when forming the conductive layer, the upstands may be made with a different ink to the rest of the conductive layer.

Accordingly, the materials from which the upstands are made could be decided based on non-electrical properties such as the rigidity and thickness of the ink when dried. When forming the insulator layer, the upstands may be made with a different insulating material to the rest of the insulator layer. Different numbers of print steps and types of inks can be used across different areas of the upstand matrix (especially for the upstands discussed above in relation to the third example). Accordingly, the different print steps can be used to create upstands that vary in height across the length and breadth of the upstand matrix. Some areas of the upstand matrix may have different underlying printed features between layers.

Concerning the third example discussed above and featured in Figure 12, if no optional insulator layer is used, the electrically non-functional upstands of the air passage layer can be deposited in line with/directly over the conductive electrode tracks, so as not to cause electrical bridging (shorting) between tracks.

In other examples, both an air passage layer such as that shown in Figure 12 is provided in addition to an air passage in the conductor layer and/or the insulator layer. Accordingly, faster venting may occur.

The sample introduction chamber may be provided along the longitudinal axis of the electrochemical device. The air passage may extend along the longitudinal axis. The air passage may then vent air in an opposite direction along the longitudinal axis to the direction in which a fluid sample is provided. In some examples, there may be more than one longitudinal air passageway. In some embodiments, an air

passageway may vent air out of a side of the electrochemical test device. In examples in which air is vented into a sealed chamber within the electrochemical test device, the chamber may be formed in any one or more of the layers of the electrochemical test device. For example, a sealed chamber may be formed during the printing of the conductor and insulator layers such that a sealed chamber is formed spanning both layers.

By controlling the ratio between the width of the air passageway and the size of the chamber, one may configure and control the sample fill volume and sample fill speed. That is, in manufacture the dimensions of the sealed chamber can be used to optimise a speed at which a fluid may enter the sample introduction channel and the volume of the sample received. The sealed chamber may extend along most of the electrochemical test strip and may be of any suitable shape. The length and width of the sealed chamber can be varied depending on the sealed chamber volume required for venting. Upstands may also be provided within the sealed chamber for supporting the other layers.

Whilst the above examples have been described primarily in the context of an electrochemical test device for measuring a concentration of an analyte in a bodily fluid, it may equally be used in other fields, for example in health and fitness, food, drink, bio-security applications and environmental sample monitoring. The above embodiments have been described by way of example only, and the described embodiments are to be considered in all respects only as illustrative and not restrictive. It will be appreciated that variations of the described embodiments may be made without departing from the scope of the invention.

Claims

Claims:

1. An electrochemical test device for determining a concentration of an analyte in a fluid sample, the electrochemical test device comprising:

a support layer;

a conductor layer above the support layer, the conductor layer comprising a set of electrodes;

a spacer layer above the conductor layer, the spacer layer defining a sample introduction channel for introducing the fluid sample to the set of electrodes; and

a cover above the spacer layer for covering the top of the sample introduction channel;

wherein the electrochemical test device comprises an air passageway for venting air from the sample introduction channel, and wherein the air passageway is formed below the spacer layer.

2. An electrochemical test device according to claim 1 , wherein the

electrochemical test device has a longitudinal axis, and the air passageway is arranged for venting air primarily in the direction of the longitudinal axis.

3. An electrochemical test device according to claim 1 or claim 2, wherein the conductor layer further comprises a set of conductive tracks, each conductive track of the set of conductive tracks being electrically coupled to a corresponding electrode of the set of electrodes.

4. An electrochemical test device according to claim 3, wherein the air passageway is disposed between conductive tracks of the set of conductive tracks.

5. An electrochemical test device according to any preceding claim, wherein a width of the air passageway is narrower than a width of the sample introduction channel.

6. An electrochemical test device according to any preceding claim, wherein the air passageway is provided with a plurality of upstands for providing a plurality of venting routes within the air passageway.

7. An electrochemical test device according to any preceding claim, wherein the lower surface of the cover has hydrophilic properties.

8. An electrochemical test device according to any preceding claim, wherein the spacer layer comprises an adhesive having hydrophobic properties.

9. An electrochemical test device according to any preceding claim, wherein the spacer layer comprises double sided adhesive tape.

10. An electrochemical test device according to any preceding claim, wherein the conductor layer is a printed layer.

11. An electrochemical test device according to any preceding claim, wherein a thickness of the conductor layer defines, at least in part, a height of the air passageway.

12. An electrochemical test device according to any preceding claim, further comprising:

an insulator layer above the conductor layer and below the spacer layer, wherein the insulator layer defines an area in which at least part of the set of electrodes is exposed to the sample introduction channel.

13. An electrochemical test device according to claim 12, wherein a thickness of the insulator layer defines, at least in part, a height of the air passageway.

14. An electrochemical test device according to any of claims 1 to 10, further comprising:

an insulator layer above the conductor layer and below the spacer layer, wherein the insulator layer defines an area in which at least part of the set of electrodes is exposed to the sample introduction channel; and

wherein the air passageway is provided by an air passage layer above the insulator layer and below the spacer layer.

15. An electrochemical test device according to any of claims 12 to 14, wherein the air passageway is provided with a plurality of upstands for providing a plurality of venting routes within the air passageway.

16. An electrochemical test device according to any of claims 12 to 15, wherein the insulator layer is a printed layer.

17. An electrochemical test device according to any preceding claim, wherein the air passageway is configured for venting air from the sample introduction channel into a sealed chamber within the electrochemical test device.

18. A method of manufacturing an electrochemical test device, the method comprising:

providing a support layer;

providing a conductor layer above the support layer, the conductor layer comprising a set of electrodes;

providing a spacer layer above the conductor layer, the spacer layer defining a sample introduction channel for introducing the fluid sample to the set of electrodes; and

providing a cover above the spacer layer for covering the top of the sample introduction channel;

19. A method according to claim 18, wherein the conductor layer further comprises a set of conductive tracks, each conductive track of the set of conductive tracks being electrically coupled to a corresponding electrode of the set of electrodes.

20. A method according to claim 18 or claim 19, wherein providing a conductor layer comprises printing the conductor layer.

21. A method according to any of claims 18 to 20, wherein the providing a spacer layer comprises applying tape.

22. A method according to any of claims 18 to 21 , wherein providing a cover comprises applying tape.

23. A method according to any of claims 18 to 22, further comprising providing an insulator layer above the conductor layer and below the spacer layer.

24. A method according to claim 23, wherein providing an insulator layer comprises printing the insulator layer.

25. A method according to claim 23 or claim 24, wherein the air passageway below the spacer layer comprises an air passage layer above the insulator layer and below the spacer layer.

26. A method according to any of claims 18 to 25, wherein the air passageway is provided with a plurality of upstands for providing a plurality of venting routes within the air passageway.